The present invention relates to metal gaskets used for providing seals, for example, between the opposed surfaces of the cylinder block and cylinder head of an engine.
In various kinds of machines, metal gaskets having a lamination structure composed of elastic metal plates have been used up to now in order to prevent leakage of air, water, oil and others. Prevailing laminated metal gaskets of this type are provided with beads at their sealing regions. Particularly, in laminated metal gaskets for use in engines typical examples of which are cylinder head gaskets and exhaust manifold gaskets, a bead plate, which is produced by forming beads by molding on an elastic metal thin plate made of e.g., SUS301, is used as an outer plate.
There have been recently proposed, in the field of engines, various laminated metal gaskets which can cope with the trends toward making of all engine parts from aluminum alloys and toward high combustion pressure, while they have laminated structures composed of several metal sheets. For instance, Japanese Patent Publication (KOKAI) Gazette No. 11-108191 (1999) discloses a laminated metal gasket having a thick intermediate plate interposed between two bead plates. In this intermediate plate, a stopper portion composed of a plurality of convex and concave portions is formed around a bore hole, thereby to improve the endurance of the stopper function relative to the beads.
Where a bead plate is used at a sealing region, the bead is normally required to have a semi-circular profile having a width of several mm and height of several hundreds xcexcm, in the case of a full bead. Therefore, there arises such a problem that the bead molding carried out by use of a thin stainless steel plate becomes precision processing and therefore high-level quality control proportionate to the precision processing is required. In addition, use of dies is essential for such bead molding so that the design, manufacture, maintenance, control, design changes of the dies involves a large number of processes as well as high cost from the trial stage to the mass production, which reflects upon the production cost of the bead plate.
The technique disclosed in Japanese Patent Publication (KOKAI) No. 11-108191 does not overcome the limit of the conventional techniques as far as use of bead plates is concerned, so that the above-mentioned cost problem is still left unsolved.
The present invention has been directed to overcoming the foregoing problems and a prime object of the invention is therefore to provide a metal gasket which has a structure having no beads so that dies for molding are no longer necessary, resulting in easy processing and which provides good cost performance and excellent sealing ability.
The above object can be achieved by a metal gasket according to the invention which comprises (i) an elastic metal plate having a base and foldedback portions each of which is formed so as to create a clearance together with the base and disposed so as to extend around a bore hole and (ii) a metal plate thicker than the elastic metal plate,
wherein the elastic metal plate and the metal plate are laminated such that the folded-back portions of the elastic metal plate face the metal plate.
According to the invention, each folded-back portion of the elastic metal plate and, more preferably, the convex-shaped portions of each folded-back portion come in contact with each lower level portion of the metal plate, thereby forming and keeping a sealing line. In addition, when the gasket is inserted between the opposed surfaces of a cylinder head and a cylinder block for instance, the folded-back portions can conform to the deformation of the cylinder head and the cylinder block, so that a gasket excellent in sealing ability can be achieved. Further, since beads which require high-precision molding processing are not used but techniques such as partial coating treatment or auxiliary bead formation are properly employed in combination for seal reinforcement, a low-cost, highly reliable gasket can be achieved.
Preferably, the invention is arranged such that the metal plate has each lower level portion at a position close to each bore hole whereas each folded-back portion of the elastic metal plate is so disposed as to face each lower level portion of the metal plate.
Preferably, the height of the folded-back portions of the elastic metal plate is greater than the level difference between the lower level portions and the base of the metal plate. With this arrangement, the folded-back portions can be surely provided with a stopper function so that the folded-back portions have good conformity with respect to the deformation of the cylinder head and the cylinder block, thereby assuring stable bore sealing surface pressure.
In the invention, it is preferable to dispose two such elastic metal plates at opposed positions with the metal plate positioned therebetween. This forms a sealing line at both sides of the metal plate to achieve further improved sealing ability.
Preferably, the outer surface of each lower level portion of the metal plate facing each folded-back portion is provided with an auxiliary bead formed from a soft material, whereas the outer surface of a part of the base of the elastic metal plate is provided with a coating portion formed from a known rubber material, the part facing the folded-back portion. By virtue of this arrangement, the sealing ability of the gasket can be further improved so that severe control for the processing accuracy of the folded-back portions can be alleviated.
In the invention, it is preferable that each folded-back portion of the elastic metal plate is composed of a multiplicity of, for instance, two smooth convex-shaped portions which are continuously formed, projecting in a direction opposite to the base. The provision of the two continuously formed convex-shaped portions allows the clearance formed between the base and the folded-back portion to be left as much as possible, so that a stable double bore sealing line can be formed by the folded-back portion. In addition, if the cylinder head and the cylinder block are deformed where the gasket is interposed between the opposed surfaces of the cylinder head and the cylinder block for instance, the folded-back portions each composed of the two convex-shaped portions conform to the deformation as a stopper portion, so that a contacting condition similar to a line contact can be established at the lower level portions of the metal plate which is the mating face with which the folded-back portions come in contact. As a result, a stable sealing effect can be achieved.
The outer surfaces of the convex-shaped portions of each folded-back portion and/or the outer surface of a part of the base which faces the convex-shaped portions may be partly coated with a known rubber material or respectively provided with an auxiliary bead made from a soft material. By combining these means, the sealing ability of the gasket can be further improved. Additionally, these means are properly used in combination, thereby alleviating severe control for the processing accuracy of the folded-back portions.